Legacy means old.

It also carries the connotation that we have something newer [to access the data].
Hence, any coding that is over eighteen months old, is, by definition, legacy.

The implication is that when the imbecilles who only know Windows come into power, they immediately declare anything on MPE i/X as legacy.

They write their own applications that sort of, mostly, work, and sometimes don't, which may or may not access "legacy" data.

They declare that the "legacy" platforms "are going away" for seven or eight years.

After they have to grudgingly accept the fact that the "legacy" platforms "are NOT going away",
the platforms they are working with also become legacy.

As to the question of "bilinguality": If you have a dream in the new language, you are immediately imminently qualified as bilingual.
In fact, most Colleges and Universities have considered proficiency programming languages sufficient to qualify for a foreign language.

I had my first dream in COBOL in 1972. However, Latin (a legacy language) was what qualified me for my BA.
And I never had a dream in Latin (quid pro quo).

</tongue in cheek>